Packaging for planar lightwave circuits

Abstract

A planar lightwave circuit device includes one or more planar lightwave circuits (PLCs) each having an optical layer deposited on a substrate, and a package base including one or more support structures for suspending the planar lightwave circuit above a portion of the package base. Each substrate has a first coefficient of thermal expansion, whereas the package base has a second coefficient of thermal expansion. The first and second coefficients of thermal expansion differ such that a change in temperature causes the support to apply one of a compressive and a tensile force to the planar lightwave circuit in a plane within or parallel to the plane of the planar lightwave circuit. The induced stress can modify the optical performance of the PLC device, e.g. to reduce the temperature sensitivity of the device and thus maintain device performance, or for providing efficient passive or dynamic tuning of the device.

1. A planar lightwave circuit device comprising:
 a planar lightwave circuit including:
 an optical layer having a lightwave circuit substantially disposed in a plane, and 
 a substrate supporting the optical layer, the substrate having a first coefficient of thermal expansion; and 
 
 stress applying means for inducing one of a compressive and a tensile stress to the optical layer in the plane thereof for modifying a performance characteristic of the planar lightwave circuit; 
 wherein the stress applying means comprises a package base including a first support structure for suspending the planar lightwave circuit above a portion of the package base, the package base having a second coefficient of thermal expansion that differs from the first coefficient of thermal expansion, whereby a change in temperature causes the first support structure to induce one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer; and 
 wherein the first support structure comprises: a first support wall portion extending from the package base to the planar lightwave circuit, and a second support wall portion extending from the package base to the planar lightwave circuit, defining a gap therebetween. 
 
   
   
     2. The planar lightwave circuit device according to  claim 1 , wherein substantially all of the induced stress is induced in the plane or parallel to the plane of the optical layer. 
   
   
     3. The PLC circuit according to  claim 1 , wherein the compressive or tensile stress causes an expansion or a contraction of the optical layer in a direction which is within the plane of the optical layer. 
   
   
     4. The planar lightwave circuit according to  claim 1 , wherein the first and second wall portions are for applying first and second forces, respectively, in different directions to each other in the plane or parallel to plane of the optical layer. 
   
   
     5. The planar lightwave circuit device according to  claim 1 , wherein the stress changes a refractive index of the optical layer to at least partially compensate for a change in refractive index caused by the change in temperature. 
   
   
     6. The planar lightwave circuit device according to  claim 5 , wherein the optical layer comprises a polymer; whereby the optical layer exhibits a negative refractive index change with temperature, which is at least partially compensated for by a positive refractive index change caused by the first support structure inducing stress in the optical layer with the change in temperature. 
   
   
     7. The planar lightwave circuit device according to  claim 1 , wherein the first and second support wall portions are arcuate. 
   
   
     8. The planar lightwave circuit device according to  claim 1 , wherein the first support structure comprises four support walls, each of the four support walls coupled to a different end of the planar lightwave circuit. 
   
   
     9. The planar lightwave circuit device according to  claim 1 , wherein the support structure comprises an annular ring. 
   
   
     10. The planar lightwave circuit device according to  claim 1 , wherein the package base and the support structure comprise a monolithic element. 
   
   
     11. The planar lightwave circuit device according to  claim 1 , further comprising planar maintaining means for reducing non-planar deformation of the planar lightwave circuit. 
   
   
     12. The planar lightwave circuit device according to  claim 11 , wherein the planar maintaining means comprises a stiffening plate forming part of the planar lightwave circuit having a third coefficient of thermal expansion coupled to the substrate opposite the optical layer. 
   
   
     13. The planar lightwave circuit device according to  claim 12 , wherein the third coefficient of thermal expansion is greater than the first coefficient of thermal expansion and less than the second coefficient of thermal expansion. 
   
   
     14. The planar lightwave circuit device according to  claim 11 , wherein the planar maintaining means comprises a second support structure mounted on the planar lightwave circuit opposite the first support structure, the second support structure including a first support wall portion for contacting the first end of the planar lightwave circuit, and a second support wall portion for contacting the second opposite end of the planar lightwave circuit, defining a gap therebetween. 
   
   
     15. The planar lightwave circuit device according to  claim 1 , wherein the stress applying means includes a heating element for adjusting the temperature of the package base causing expansion or contraction thereof for applying stress to the planar lightwave circuit for dynamic tuning of a performance characteristics selected from the group consisting of refractive index, birefringence, wavelength shift, insertion loss, and optical mode profile control. 
   
   
     16. The planar lightwave circuit device according to  claim 15 , wherein the heating element comprises a Peltier heating element having a hot side and a cold side; wherein the hot side is adjacent the package base for applying a refractive index change to the optical layer. 
   
   
     17. The planar lightwave circuit device according to  claim 15 , wherein the heating element comprises a Peltier heating element having a hot side and a cold side; wherein the cold side is adjacent the package base for applying a refractive index change to the optical layer. 
   
   
     18. The planar lightwave circuit device according to  claim 1 , wherein the stress applying means includes a package base with a first support structure, which is pre-stressed relative to the planar lightwave circuit by attaching the planar lightwave circuit to the package base at a higher or lower temperature than room temperature or other operating temperature of the planar lightwave circuit, whereby at ambient temperature the first support structure induces one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer. 
   
   
     19. The planar lightwave circuit device according to  claim 1 , wherein the stress applying means comprises mechanical stressing means for applying one of a compressive and a tensile force in the plane or parallel to the plane of the planar optical layer for dynamic tuning of a performance characteristics selected from the group consisting of birefringence, wavelength shift, insertion loss, and optical mode profile control. 
   
   
     20. The planar lightwave circuit device according to  claim 1 , wherein the first support structure comprises four support walls, each of the four support walls coupled to a different portion of the planar lightwave circuit. 
   
   
     21. A planar lightwave circuit device comprising:
 a planar lightwave circuit including:
 an optical layer having a lightwave circuit substantially disposed in a plane, and 
 a substrate supporting the optical layer, the substrate having a first coefficient of thermal expansion; and 
 
 stress applying means for inducing one of a compressive and a tensile stress to the optical layer in the plane thereof for modifying a performance characteristic of the planar lightwave circuit; 
 wherein the stress applying means comprises a package base including a first support structure for suspending the planar lightwave circuit above a portion of the package base, the package base having a second coefficient of thermal expansion that differs from the first coefficient of thermal expansion, whereby a change in temperature causes the first support structure to induce one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer; and 
 wherein the first support structure comprises: a first support wall portion extending from the package base to the planar lightwave circuit, and a second support wall portion extending from the package base to the planar lightwave circuit, defining a gap therebetween; 
 further comprising planar maintaining means for reducing non-planar deformation of the planar lightwave circuit; 
 wherein the planar maintaining means comprises supporting rib means extending from the package base into contact with the planar lightwave circuit between the first and second supporting wall portions; wherein the planar lightwave circuit is freely floating on the supporting rib for minimizing non-planar deformation. 
 
   
   
     22. The planar lightwave circuit device according to  claim 21 , wherein the supporting rib means comprises one or more of the supporting ribs selected from the group consisting of: a transverse rib extending substantially parallel to the first and second supporting wall portions, a longitudinal rib extending substantially perpendicular to the first and second supporting wall portions, a solid pedestal rib, and a hollow pedestal rib. 
   
   
     23. A planar lightwave circuit device comprising:
 a planar lightwave circuit including:
 an optical layer having a lightwave circuit substantially disposed in a plane, and 
 a substrate supporting the optical layer, the substrate having a first coefficient of thermal expansion; and 
 
 stress applying means for inducing one of a compressive and a tensile stress to the optical layer in the plane thereof for modifying a performance characteristic of the planar lightwave circuit; 
 wherein the stress applying means comprises a package base including a first support structure for suspending the planar lightwave circuit above a portion of the package base, the package base having a second coefficient of thermal expansion that differs from the first coefficient of thermal expansion, whereby a change in temperature causes the first support structure to induce one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer; and 
 further comprising an additional planar lightwave circuit mounted on the package base, the additional planar lightwave circuit including an optical layer having a lightwave circuit, and a substrate supporting the optical layer, the substrate having a coefficient of thermal expansion different than the first or the second coefficient of thermal expansion, whereby a change in temperature results in the package base inducing a different amount of stress to the different planar lightwave circuits. 
 
   
   
     24. A method of modifying a performance characteristic of a planar lightwave circuit including: an optical layer having a lightwave circuit defining a plane, and a substrate supporting the optical layer, the substrate having a first coefficient of thermal expansion, the method comprising the steps of:
 a) inducing one of a compressive and a tensile stress for modifying a performance characteristic of the planar lightwave circuit; wherein substantially all of the applied stress is induced in the plane or parallel to the plane of the optical layer 
 wherein step a) comprises mounting the planar lightwave circuit onto packaging; and 
 wherein the packaging comprises a package base including a first support structure for suspending the planar lightwave circuit above a portion of the package base, the package base having a second coefficient of thermal expansion that differs from the first coefficient of thermal expansion, whereby a change in temperature causes the first support structure to induce one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer 
 wherein the first support structure comprises a first support wall portion extending from the package base to the planar lightwave circuit, and a second support wall portion extending from the package base to the planar lightwave circuit, defining a gap therebetween. 
 
   
   
     25. The method according to  claim 24 , wherein the stress changes a refractive index of the optical layer to at least partially compensate for a change in refractive index caused by the change in temperature. 
   
   
     26. The method according to  claim 24 , further comprising the step of reducing non-planar deformation of the planar lightwave circuit. 
   
   
     27. The method according to  claim 26 , wherein the step of reducing non-planar deformation comprises mounting a second support structure on the planar lightwave circuit opposite the first support structure, the second support structure including a first support wall portion for contacting the first end of the planar lightwave circuit, and a second support wall portion for contacting the second opposite end of the planar lightwave circuit, defining a gap therebetween. 
   
   
     28. The method according to  claim 26 , wherein the step of reducing non-planar deformation comprises providing planar maintaining means;
 wherein the planar maintaining means comprises supporting rib means extending from the package base into contact with the planar lightwave circuit between the first and second supporting wall portions; wherein the planar lightwave circuit is freely floating on 
 the supporting rib for minimizing non-planar deformation. 
 
   
   
     29. The method according to  claim 24 , wherein step a) includes adjusting the temperature of the package base causing expansion or contraction thereof for inducing stress in the planar lightwave circuit for dynamic tuning of a performance characteristic selected from the group consisting of refractive index, birefringence, wavelength shift, insertion loss, and optical mode profile control. 
   
   
     30. The method according to  claim 24 , wherein step a) includes pre-stressing the package base relative to the planar lightwave circuit by attaching the planar lightwave circuit to the package base at a higher or lower temperature than room temperature or other operating temperature of the planar lightwave circuit, whereby at ambient temperature the first support structure induces one of a compressive and a tensile stress in the plane or parallel to the plane of the optical layer.